The present invention relates generally to a warm up control system for an internal combustion engine for effectively warming up the engine when the engine is started under cold engine conditions. More specifically, the invention relates to an electronic control system for warming up of the internal combustion engine providing effective warm up characteristics of the engine by controlling the engine operating conditions to the maximum idle engine speed with the maximum engine stability.
Recently, there have been developed various electronic engine control system for the purpose of fuel economy, maximum engine output efficiency, improving drivability and/or minimizing of emission and fuel consumption. For the engine warm up from a cold start, an engine control effected by electronic control systems are preferably in order to improve warm efficiency with the minimum fuel consumption and exhaust emission. It is required for engine warm up operation under cold engine conditions, to feedback control the engine speed corresponding to the engine temperature and engine stability. The intake air flow rate in the engine warm up condition, and spark ignition timing are therefore to be controlled for bringing the engine speed to a predetermined value based on the engine temperature and engine driving stability.
For warming up during the engine idling condition, as is well-known, the intake air is supplied through an auxiliary induction passage bypassing the throttle valve. The auxiliary induction passage is provided with an electromagnetically operable idle air control valve so that it can control the air flow rate flowing therethrough to adapt the actual engine speed to the predetermined value. Also, the spark ignition timing is controlled for maximum engine warm up efficiency with desirable engine operating conditions. In the disclosure, the wording "engine warm up efficiency" or "engine warm up rate" is used to represent an engine temperature variation speed form warm-up under cold engine conditions. Therefore, the engine warm up efficiency or the engine warm up rate may be considered as the engine warm up speed which is variable depending on the engine speed. To obtain fast engine warm up speed, relatively high engine speed is required. On the other hand, by the high engine speed under substantial cold engine conditions, emission cannot be satisfactorily controlled due to the inactive state of the exhaust gas purifier.